The invention relates to programmable drug infusion pumps.
Infusion pumps as used in the field of health care are electromechanical devices which control the flow rate of medical fluids. An example of a drug infusion pump is the AS40A.RTM. Infusion Pump by Baxter Healthcare Inc. It operates a medical syringe to deliver a drug to a patient at a precisely controlled rate. The AS40A employs an active fluid pumping mechanism, i.e., positive displacement of the syringe plunger, to expel fluid from the syringe. This type of pump is generally known as a syringe pump.
A vital application for infusion pumps in the human and veterinary medical field is in the delivery of chemicals, drugs, nutrition, or biological products to patients. Typically, in these applications, one or more drugs or other substances are mixed into a uniform solution in a medical fluid and are then delivered through an infusion pump into the bloodstream of a recipient via tubing and/or catheters which conduct the fluid from the pump to the recipient's vascular space.
The fluid flow rate or sequence of rates at which an infusion pump operates are typically selected based on a desired pattern of drug delivery appropriate to the specific circumstance. There are numerous factors that should be considered in the process of specifying a specific rate of fluid flow from a pump at a particular moment in time. Those factors may include:
(i) the nature of the substance being infused, including the known pharmacokinetics and pharmacodynamics of a drug; PA0 (ii) the concentration or dilution of the substance in the fluid; PA0 (iii) the recipient, including sex, age, various measures of weight or size, the state of function of various organ systems, and ability to tolerate infusion of various diluent fluid volumes; PA0 (iv) the occurrence of change in measurable endpoints related to the actions or effects of the substance being infused; PA0 (v) the difference between the estimated concentration of the drug at the target site of drug action (as computed based upon actual measurements or based upon pharmacokinetic models and the prior history of the infusion and/or other factors), as compared to the desired concentration; PA0 (vi) local practices, policies, protocols, and regulations; or PA0 (vii) other considerations including operator judgement.
The process by which a patient care-giver takes the above considerations into account and chooses fluid flow rates for drug delivery from a pump is complex and if done incorrectly can lead to serious problems. The process is prone to error, especially because of the requirement for multiple computations and calculations. The complexities are aggravated by several factors. The staff training cost and the cost of preparing, updating, and distributing formularies and policy and procedure protocols within hospitals is large. The difficulty of establishing safe and uniform practices is compounded by significant local, regional, and nation-to-nation variations in practice patterns. The complexity of using such pumps may result in denial of needed therapy to patients because a care-giver lacks sufficient training, or does not have ready access or the time to review relevant knowledge or to use other tools (such as computational devices) to effect the process of delivering a needed medication infusion to a specific patient.
Various technological approaches have been taken in the past to make infusion pumps more suitable for intravenous drug infusions. For example, companies have developed calculator-type infusion pumps which allow users to deliver drug diluted in a fluid by entering data such as drug concentration, patient weight, and desired doses and dose rates using dose delivery units such as mcg/kg or mcg/kg/min. Based upon these inputs, the pumps calculate the volumes and fluid flow rates to be delivered.
Some pumps include physical templates which can be attached to and which electromagnetically modify (i.e., program) the infusion pump. These templates are drug-, drug-concentration-, drug-container-size-, bolus-rate-, and dose-delivery-unit-specific. The templates contain knowledge which is useful for end-users in that typical drug delivery doses and dose rates are printed on the physical templates. For each drug delivery configuration there must be a separate template. In addition, if a particular drug delivery configuration will be used simultaneously on multiple pumps within a facility, there must be available an equal number of identical templates, one for each pump.
Other approaches to making fluid infusion pumps more suitable for drug infusion have included the development of pumps which contain digital communication ports for external control. These permit the infusion pump to be continuously cabled to a separate remote personal computing device. The personal computer can then run a particular program tailored to provide the desired pattern of drug delivery appropriate to the specific circumstance.
Still other approaches to making fluid infusion pumps more suitable for drug infusion have included the development of pumps which contain microprocessor controllers and EPROM devices containing preprogrammed information including a series of drug infusion profiles relating to various drugs to be infused (See PCT International Publication No. WO 88/10383 entitled "Infusion Pump and Drive Systems Therefore"). A related approach, which is described by Crankshaw et al. in U.S. Pat. No. 4,741,732, involves use of EPROM modules which can be physically plugged into the pump casing. The modules are drug-specific and thus a separate module is required for each drug type. The program within a module varies the infusion rate over time according to a predefined drug delivery profile algorithm.